318 



INSECTA. 



idea of a delicate bag having the power of distending itself : its mus- 

 cular walls might indeed contract ; but that a thin sacculus should forci- 

 bly expand itself would be a fact new to physiology. 



(834.) The gizzard is found in insects which possess mandibles and 

 live upon solid animal or vegetable substances. It is a small round 

 cavity with very strong muscular parietes, situated just above the 

 stomach properly so called, and, like the gizzard of granivorous birds, 

 is employed for the comminution of the food preparatory to its intro- 

 duction into the digestive stomach. In order to effect this, it is lined 

 internally with a dense cuticular membrane, and occasionally studded 

 with hard plates of horn, or strong hooked teeth, adapted to crush or 

 tear in pieces whatever is submitted to their action. 



(835.) When bruised in the gizzard, the food passes on into the proper 

 stomach, which is generally a long intestiniform organ (fig. 159, d d), 

 extending from the crop or gizzard to the point where the biliary vessels 

 discharge themselves into the 



intestine. The size and shape Fig. 160. 



of this organ will vary, of 

 course, with the nature of the 

 food. Thus, in the Butterfly, 

 which scarcely eats at all, 

 or sparingly sips the honey 

 from the flowers, it is very 

 minute (fig. 160, 6) ; but in 

 insects which live upon coarse 

 and indigestible materials, it 

 is proportionately elongated 

 and capacious. 



(836.) The stomach gene- 

 rally ends in the small in- 



J 



but this is occasionally en- 

 tirely wanting, so that the 

 stomach seems to terminate 

 immediately in the colon or 

 large intestine, which is the 

 terminal portion of the ali- 

 mentary canal: when much 

 developed, the small intestine 

 is sometimes divided by a 

 constriction into two parts, 

 to which the names of duodenum and ilium have been applied by ento- 

 mological writers. The colon (fig. 159, / ; fig. 160, Te) is separated from 

 the small intestine by a distinct valve ; and in connexion with its com- 

 mencement a wide blind sacculus or caecum is often met with. 



Alimentary canal of a Butterfly : a a, proboscis ; p, 

 mouth ; m m, pharynx ; sp, s p, salivary glands ; o, oeso- 

 phagus ; v v, crop, communicating by a canal (c,/) with 

 the stomach proper (b, z) ; i, small intestine ; k, large 

 intestine ; g g g, hepatic vessels ; h, n, their termina- 

 tions in the vicinity of the pylorus. 



